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The behaviour of an energy pile in a group is different from that of an isolated energy pile due to thermal and mechanical interactions. This study aims to extend the load transfer method to consider the mechanical and thermal interactions of energy piles in groups. The load displacement curve of an energy pile in a group is modified from that of the isolated pile through a displacement factor to account for group effects. This paper presents the results of a full-scale field test of four operating energy piles over 12 months, against which the proposed method is validated. Temperature changes of ∆T = 5, 10, 15, 20 °C were applied in the analyses. A comparison between the experimental and numerical results reveals the capability of the approach to provide information about the vertical displacement, vertical stress, and mobilised shaft resistance profile for an energy pile in a group subjected to both mechanical and heating thermal loads.

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Thermally induced group effects characterise closely spaced energy piles. It has been observed experimentally that the behaviour of energy piles subjected to mechanical and thermal loads, in which the piles are located sufficiently close to each other, is different from the behaviour of single isolated piles. Therefore, civil engineers encounter new challenges in the geotechnical design of such foundations. This leads to the necessity to develop practical tools to address their analysis and design. The conventional load transfer method is one of the commonly used methods for the analysis of axially loaded conventional piles. Thus, the purpose of this study has been to propose a formulation of the load transfer method to consider the thermally induced effects among energy piles in groups. The soil response is characterized in a lumped form by ascribing the behavioural features of the soil to interface elements. The individual response, in terms of strain and stress of an energy pile in a group, can be addressed for the first time through the application of the displacement factor in the load displacement curve of the single isolated energy pile. A validation through a full-scale field test reveals the capability of the approach to provide the necessary information in the analysis and design phases of the foundation for one-way thermal loads.